Marek’s Disease in Backyard Chickens

By Barry Whitworth

Raising backyard chickens has become very popular in Oklahoma. Some people desire a better understanding of how their food is produced. Others like the rewarding experience of going out in the backyard and gathering eggs. However, many backyard producers may not be aware of a disease that might threaten their chickens. According to Keith Bailey, DVM, director of the Oklahoma Animal Disease Diagnostic Laboratory (OADDL), Marek’s disease (MD) was the most common disease diagnosed in chickens submitted to the lab for necropsy in 2015-2016.

The first report of the disease was in 1907 by József Marek, hence the name Marek’s disease. Since that initial discovery, the disease has been found worldwide and is a major problem with chicken production. Marek’s disease is caused by a highly contagious herpes virus called alphaherpesverinae. The virus can invade the body and survive without being destroyed by the immune system. The virus infects certain white blood cells causing a few of the cells to become cancerous. These cells can infiltrate internal organs (kidneys, liver, gonads, and proventriculus), peripheral nerves, skin, and muscles.

Transmission of the virus occurs by direct and indirect contact between chickens. The virus replicates in the feather follicles and is shed into the environment in the dander from the chickens. This dander contaminates the facilities and remains infectious for several months. Chickens become infected by inhaling the virus. Once the virus is in the flock, it spreads rapidly from bird to bird even if the chickens are vaccinated. The virus may also be spread by people or equipment that has been contaminated with chicken litter. Darkling beetles and mealworms may carry the virus, too. Transmission of the virus from hen to chick through eggs is highly unlikely since the virus should not be able to survive the temperature and humidity levels required to incubate eggs.

Learn more in the April issue of OKFR!